Making planes safer and cheaper

Press release issued:
29 April 2002

UNIVERSITY OF BRISTOL Media release Making planes safer and cheaper

Aircraft could become safer and cheaper thanks to pioneering work at the University of Bristol. Engineers in the Aerospace Department have been awarded two grants totalling more than £600,000 from the Engineering and Physical Sciences Research Council to address some of the complex problems involved.

One way to make cheaper planes is to use materials for aerospace structures that are light but strong. This improves fuel efficiency and thereby increases the distance travelled for the same amount of money.

Increasingly the aerospace industry is using composite materials to make aircraft parts. These materials, such as carbon fibre, combine several different substances to yield characteristics superior to those of the individual constituents. They can be very light and stronger than steel, but it is not fully understood how they respond when, for example, a hole is drilled into them.

A further complication, shown by initial work at the University, is that there is a significant reduction in strength with increasing size. This means that a substantial amount of full-size testing is still required which is very expensive - more than £10 million for a typical aircraft. As a consequence, large safety margins are built in to compensate for uncertainties, resulting in expensive and overweight aircraft.

Professor Michael Wisnom at the University of Bristol will be leading a project to look at how composite materials behave when they contain holes or cracks, and the problems of applying small-scale results to full-size aircraft.

Professor Wisnom said: 'If tests could be done on small-scale samples of these materials and the results applied to the larger scale with greater confidence, it would mean much lower costs and more reliable composite structures.'

Another way to improve safety is to gain a greater understanding of the stresses that aircraft are subjected to, so that potentially dangerous situations can be realistically modelled on a computer without having to destroy expensive equipment.

Dr Chris Allen, recently awarded the Kenneth Harris James Prize for his aerospace research, will be leading investigations at the University into these aspects of flight safety.

Civil aircraft usually travel at transonic speeds - just below supersonic. But when a wing is subjected to a disturbance at these speeds - a strong gust of wind, for example - it may become unstable and the disturbance will grow until the wing eventually breaks. The accurate simulation of these unsteady responses for real aircraft is clearly of fundamental importance to the aerospace industry.

Although it is no longer necessary to put a plane into a wind tunnel to simulate these effects, the computational power required to do this work is very expensive and has only recently become available. Even with today's computers it can take several months to solve all the equations involved.

Dr Allen said: 'Once this is understood the team plans to design flight controls that will suppress these effects to ensure the wing remains stable. Increasing the stability means the wing can be made less stiff and therefore lighter.'

The two projects will be part-funded by aerospace companies Airbus UK, Dowty Propellers and BAE Systems, all of whom stand to gain important information from the results. Hexcel Composites will provide the composite materials.